Field of Invention
This disclosure is related to methods and systems for processing a substrate and more specifically to methods and systems for controlling etch rate drift and creation of particles during plasma processing.
Description of Related Art
Chamber wall materials/coatings are critical in high density plasma process with heavily reactive and corrosive feed gas. Very often, the plasma process is very sensitive to the surface changes of chamber wall materials/coatings with time (or radio frequency (RF) time). Some chamber wall materials/coatings, (e.g. Yttrium based materials or coatings), can run extended RF hours, (for example, greater than thousand RF hours) compared to others, (e.g. anodized Al), which may only run a couple of hundred RF hours. Also, some chamber wall materials/coatings can more easily generate particles compared to other materials/coatings. Furthermore, the surface change of the chamber wall materials/coatings may even change the RF current return or affect the plasma species like radical concentrations, plasma density, or other plasma parameters, which then cause significant process drift, (e.g. etch rate drift), or chamber matching.
So far, yttrium based coatings, mainly Y2O3 coatings have been widely used in plasma process tools as a chamber coating material due to its high resistance to erosion and corrosion, especially in metal or gate etch processes which involve heavily Cl2/O2 or HBr/O2 plasmas. However, in some processes, particles originated from Y2O3 coatings have been recognized to be a big issue especially as the lines or features become smaller and smaller. These particles may cause device and process failure. Also, wafer-less dry clean or wet clean are not the solution to eliminate the particle generation during the plasma process. Alternatively, YF3 coating instead of Y2O3 coatings has been used to suppress the particle generation. However, while it has successfully suppressed the particle generation, other issues appeared. It has been found that the etch rate drifted or decreased significantly with fresh or cleaned chamber walls and it requires extended dummy runs to season the chamber walls in order to have an acceptable and stable etch rate. There are no clear solutions on the Y2O3 particle issue and YF3 etch rate drift issue so far due to lack of understanding of the mechanisms of the particle formation and etch rate drift.
There is a need for an understanding of the mechanism and pathways that cause the particle formation and etch rate drift issues. With this understanding, a system and method for controlling creation of particles and etch rate drift during plasma processing can be developed and implemented.